Feissel



March 8, 1960 H. FEISSEL PULSE CODE MODULATION DEMODULATOR Original Filed Oct. 25, 194 8 2 Sheets-Sheet 1 pzuzyzwg 7 34 D/JTR/BUTOR ATTORNEY 2 Sheets-Sheet 2 March 8, 1960 H. FEISSEL PULSE CODE MODULATION DEMODULATOR Original Filed Oct. 23, 1948 United States Patent 'PULSE coon MODULATION DEMODULATOR Henri Feissel, Paris, France, assignor to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Original No. 2,651,716, dated September 8, 1953, Serial No. 56,243, October 23, 1948. Application for reissue May 6, 1955, Serial No. 506,682

Claims priority, application France November 8, 1947 6 Claims. (Cl. 250-27) Matter enclosed in heavy brackets II appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

The present invention relates to impulse transmission systems and more particularly to a system for translating amplitude modulated pulses into coded pulse groups.

It is an object of the invention to provide an improved and simplified pulse code modulation modulator and an improved and simplified pulse code modulation demodulator.

The above mentioned and other features and objects of the invention will become more apparent and the invention itself, though not necessarily defined by said features and objects, will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings wherein:

Figs. 1 and 2 are sets of curves useful for the understanding of the invention;

Fig. 3 is a block diagram of a coding arrangement incorporating features of the invention;

Fig. 4 is a block and schematic diagram of a receiving circuit for the coded impulses transmittedby the device shown in Fig. 3.

Referring to Fig. 1, I show a modulating signal and a sequence of impulses modulated in amplitude according to said signal. It will be assumed in order to facilitate the description that the amplitudes of these impulses vary between two reference levels, 0 and 1.

According to a feature of the invention, a certain combination of constant amplitude impulses are transmitted in time sequence for each amplitude modulated impulse. The signals transmitted are characterized by the fact that impulses are or are not transmitted at given instants. It is known that the possible number of combinations of such a code comprising a maximum of n impulses is equal to 2". To this effect the first impulse is made to correspond to the implitude la, the second to amplitude M, the third to amplitude A; and the 11 to amplitude Ma For any given amplitude comprised between the reference levels 0 to 1 it is thus possible to find a code combination of n pulses corresponding to the said amplitude with an approximation of la.

The purposeof the coding arrangement is to translate an impulse of a given level into the corresponding nearest code combination of constant amplitude impulses, and the purpose of the decoder is to translate said code combination into single impulse whose level approximates the amplitude of the original impulse.

According to a preferred embodiment of the invention a coding arrangement will now be described.

Let I be an impulse of level N comprised between two reference levels 0 to 1. The amplitude N is compared to level V2; if N, is greater than /6 a first code impulse is transmitted and an impulse I, of level 2 N =2(N /z) is produced. If N, is less than no first code impulse is transmitted and an impulse I: of level N =2N is transmitted to the following stage. In either case the impulse N transmitted to the next stage is comprised between 0 and 1.

The impulse of amplitude N is then compared to level /i. If N: is greater than /2 a second code impulse is transmitted and an impulse I of level N =2(N /z), is produced. If N, is less than /a no second code impulse is transmitted and an impulse I; of amplitude N =2N is transmitted to the next stage. In both cases N is comprised between 0 and 1. This process is repeated n times, at which time the desired degree of ap# proximation is attained.

The operation of the coding arrangement will be better understood from the following description of the embodiment shown in Fig. 3, which represents a coding arrangement for a 5 unit code.

This coding arrangement comprises a modulator-distributor 1 to which are connected a number of transmission channels 2, for example voice frequency telephone channels. The modulator-distributor produces on line 3 reference impulses which are used for synchronization and on line 4 amplitude modulated impulses which are directed respectively to devices 5, 6, 7, 8 and 17 which are provided for translating amplitude modulated impulses into coded pulse groups.

Each of the devices 5, 6, 7 and 8 comprises a delay line 9 for delaying the impulses by a length of time equal to the time interval separating two successive coded in!- pulses. Each also comprises a threshold amplifier 10 with a voltage amplification equal to 2 and arranged such that it amplifies the fraction of the input impulse applied to it which exceeds the one-half level. Each of the devices 5, 6, 7 and 8 also comprises a limiteramplifier 11 which limits the amplitude of the impulse from 10 to a constant level chosen for the coded impulses. Each also comprises an amplifier 12 with a voltage amplification equal to 2 associated with a blocking device which operates under the action of an impulse from 11. The blocking device is provided so that amplifier 12 is blocked for a. duration overlapping the retarded impulse from 1. This may be obtained by a delay line or a time constant device for widening the blocking impulse applied from 11.

A delay line 13, similar to delay line 9, is provided after the threshold amplifier 10 to delay the impulses going through it by a length of time equal to the time interval which separates two successive coded impulses.

There are thus four identical arrangements, each corn prising elements such as 9, 10, 11, 12 and 13 which have just been described. The last stage 17 is a limiter-amplifier which, similarly to the preceding circuit 10, comprises a threshold device which lets through or not the fifth code impulse according to whether the impulse coming from circuit 8 is greater or smaller than the one-half reference level. A mixer 14 mixes the synchronizing impulses from 3 and the coded impulses from devices 5, 6, 7, 8 and 17.

Referring again to Fig. 1, I show a set of amplitude modulated impulses and the envelope of these impulses which are comprised between the reference levels 0 and l.-' As an example two impulses M and N of respective amplitudes 0.43 and 0.66 have been shown respectively below and above the one-half reference level. The corresponding coded impulses are shown in Fig. 2. The time interval T during which the coded impulses are trans mitted is shown as AB. This time interval is divided into five equal intervals which are called elementary in-' tervals 1, 2, 3, 4, 5 (in the case of a 5 element code); According to the code combination one impulse isoris not transmitted during each elementary interval.

When an impulse is transmitted in the third time in "(equal to 0.66).

The impulse M; of amplitude 0.43 which reaches cir- "c'uit o'fFig. 3 cannot pass through amplifier since its level is less than one-half. The first impulse is not transmitted and impulse M is delayed by delay line and itsamplitude doubled by amplifier 12. (lt'reaches the "following circuit 6 during the second elementary time intervalwith an amplitude equal to 0.86, i.e. with an amplitude greater than one-half reference level, and therefore passesthrough'the threshold amplifier 10. A code impulse is transmitted in position 2, and an impulse with an amplitude 2(0.860.5)=0.72' is transmitted to circuit 7"thr'ough delay line 13. This impulse reaches the following circuit 7 during the third elementarytime interval, with an amplitude equal to 2 ().36=0.72. An impulse is""transmitted by this circuit 7 in position 3, since the level applied to it exceeds the onehalf reference level. On'the contrary, the impulse transmitted to the next circuit 8 has an amplitude equal to 2(0.72'O.5)=0.44 i.e.', it'is'lessthan one-half, and no code impulse is transmittcdin position 4. This impulse is amplitude doubled and applied with a'level of 0.88 to the final limiter device '17 which" lets an impulse pass into position 5 since the level exceeds the one-half reference level. It may be noted that a distinguishing feature of'the coder is that the refeience level remains constant on each comparison.

' The code combination transmitted is that .shown in the upper part of Fig. 2. It is easily seen that in the case of impulse N of 'Fig. l, which has an amplitude of 0.66, coded impulses are transmitted in positions '1, 3 and 5 as "shown on the bottom part of Fig. 2.

The duration of the coded impulses depends upon the operating conditions of the transmitter. They may be very narrow or broad enough for two successive impulses to'be adjacent.

-Fig. 4 shows an example of an embodiment of a decoding arrangement adapted to transform a set of coded impulses into an impulse whose amplitude is approximately equal to that of the original amplitude modulated impulse. This arrangement is designed for a 5 unit code,

but may be extended to a code comprising more or less thanS elements.

' .Itcomprises for instance a distributor 19 which receives from line 20 the reference or synchronising impulses and he -coded impulses. This distributor, which maybe of any known type, distributes the successive coded impulses belonging to the same group to wires 21, 22, 23, 24 and 25. Delay lines 26, 27, 28 and 29 are respectively provided on each wire, in such a way that these coded impulses reach respectively wires 30, 31, 32, 33 and at the same moment. The impulse on wire 25 is the last impulse leaving the distributor and does not need to befldelayed. I The delay line 29 delays the impulse which flow through it by length of time equal to the time intervalseparatingtwo successive coded impulses; delay line delays the impulses which flow through it by a length of time equal to the time interval elapsing between three consecutive coded impulses, and so on. These impulses therefore reach the control grids of the vacuum tubes 34, 35,36, 37-and 38 at the same time. The cathode resistances 39, 40, 41, 42 and 43 of these tubesareof such a value that the plate current in the respective vacuum tubes :is proportional-to the level corresponding to the impulse with which it is associated. All these currents add together in the plate resistance of the vacuum tube, which .is connected-on the onehand to the plate of the tubes, and on' the other hand to .a sourceof high potential 45. -In-this-way animpulse is obtained on wire 46 whose amplitude is approximately equal to that of the initial amplitude modulated pulse. A device (not shown) is used for directing to their respective channels the modulated impulses leaving the decoder according to a well known technique, where they are used to regulate the original modulating currents.

While I have described a particular embodiment of my invention for the purposes of illustration, it should "be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the appended claims.

What is claimed is:

1. An electrical translator for converting sequential pulses in each of a plurality of sequentiallytimed pulse code groups into [to] corresponding amplitude modulated pulses comprising delay means forthe individual pulses of each said code group to cause said individual pulses to be equally timed, a combining circuit, said combining circuit comprising [a plurality of amplifiers of different gains] means for adjusting the amplitudes 'of said "individual pulses in accordance with a predeterminedicode, means for applying said equally timed pulses to said combining circuit and means for adding together said pulses at the outputs of said [amplifiers] means.

2. An electrical translator according to c laiml wherein said delay means comprises a distributor and a plurality of delay devices each connected to an output circuit of said distributor.

3. An electrical translator according to claim 1 wherein said means for adjusting the amplitudes comprises amplifiers each [comprise] includes a vacuumtube each having its gain adjusted in'accordance with said code.

4. In acommunicationsystema terminal for receiving time division multiplex code groups of signals represenb ing a'signaling wave, a plurality of delay lines, multiplex distributing apparatus for distributing received signals to a plurality of said delay lines, each of said lines having difierent delay intervals so related to each other andto said multiplex distributing apparatus that the signals" of each multiplex group applied to said delay lines arrive at their output terminals substantially simultaneously rind means for reconstructing a series of pulses corresponding to the signaling wave from said simultaneously occurring signaling conditions,

5. In a communication system, a terminal for receiving time division multiplex code groups of signals, a time delay device for each signal of a code group of signals, a multiplex distributor for distributing received signals of each code .group 'to said delay devices, said delay devices having delay intervals so related toeach other and to said multiplex distributing apparatus that the signals of each multi lex group applied to their inputs in successions arrive at the output terminals substantiollysimuh tane'ously and combining means for combining 'said'output signals from said delay devices into a singlee'lectrical output.

6. In a communication system, a terminal for recciving time division multiplex code groups of signalsfitime References Cited'in the file of this patent or the original :patent UNITED STATES PATENTS 1951;454 "Tiefenbacher Mar. 20, 1934' (Other references on following -page) pulse, the succession 5 6 UNITED STATES PATENTS 2,438,908 Goodall Apr. 6, 1948 2,145,332 Bedford Jan, 31, 193 2,4 llaeh J n 15, 1948 2,272,070 Reeves Feb. 3, 1942 67 G d Sept- 9 8 2,361,766 Hadekel Oct. 31, 1944 2,451,044 Pierce Oct. 12, 1948 2,401,405 Bedford June 4, 1946 5 2,453,454 Norwine Nov.9, 1948 2,403,561 Smith July 9, 1946 2,453,461 Schelleng Nov. 9, 1948 2,409,229 Smith Oct. 15, 1946 2,465,840 Blumlein Mar. 29, 1949 2,437,707 Pierce Mar. 16, 1948 

